This invention relates to an apparatus for emptying or discharging chip silos or the like by means of a screw conveyor disposed on the bottom or floor of the silo. The conveyor rotates about its own axis in the usual manner and also in a horizontal plane or about a conical surface of revolution to convey the chip material to a central discharge shaft, which is closed or sealed off except for an opening approximating the cross-sectional area of the conveyor screw by a generally cylindrical cover which itself rotates together with the screw conveyor. The cover is spiral-shaped in cross-section, and the step or break between the largest and the smallest radii thereof lies in the plane of the screw conveyor axis whereby the radius of the cover continually increases in the direction of its rotation.
The basic object of the invention is to further develop and improve known devices of this type, such as that disclosed in Swiss Pat. No. 516457. Although such a prior art apparatus generally performs satisfactorily, under certain conditions, particularly when fine and/or very moist chips are being discharged, the cover which rotates with the screw conveyor about a vertical axis tends to bind against the surrounding chips. This is due to the compression of the chip column in the silo, which forces them against the sides of the cover so that they exert a strong braking effect thereon in the manner of brake shoes on a brake drum. This braking effect can, in an extreme case, become so great that the rotating cover and screw conveyor are brought to a complete halt.